To realize the extension of this terraced house, an in-situ cast concrete slab was provided, as it can act as a fully isotropic plate, distributing loads efficiently to the available support points. Since the slab was chemically anchored into the existing house, its thickness could be limited to just 13 cm, and only a single steel column was required along the entire length of the stepped rear façade, allowing the façade to be designed as openly as possible towards the garden. On the street side, the characteristic bay window was entirely rebuilt to meet contemporary energy performance standards.